JPH08269608A - High strength aluminum alloy excellent in formability and corrosion resistance - Google Patents

Abstract

PURPOSE: To produce a high strength Al alloy excellent in formability and corrosion resistance by specifying its compsn. constituted of Si, Mg, Cu, Cr and Al and limiting the content of Mn as impurities. CONSTITUTION: This Al alloy is the one having a compsn. contg., by weight, 0.5 to 1.6% Si, 0.9 top 1.5% Mg and 1.2 to 2.4% Cu so as to satisfy 3<=Si+Mg+ Cu<=4%, Mg<=1.7×Si and Cu/2<=Mg<=Cu/2+0.6%, furthermore contg. 0.02 to 0.4% Cr, moreover contg., at need, one or more kinds among 0.03 to 0.2% Zr, 0.03 to 0.2% V and 0.03 to 2.0% Zn or one or two kinds of 0.005 to 0.1% Ti and 1 to 50ppm B, in which the content of Mn as impurities is limited to <=0.05%, and the balance Al with inevitable impurities, and in the structure, preferably, the precipitates of intermetallic compounds having <=0.01μm diameter and <=0.3μm length are distributed by >=2000 pieces/μm<2> . Moreover, the Al alloy is subjected to prescribed solution treatment, hardening treatment, aging treatment and heat treatment according to necessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength aluminum alloy excellent in formability and corrosion resistance, and particularly to an aluminum alloy excellent in formability, corrosion resistance and strength, which is preferably used as an outer plate or structural material of transportation equipment. .

[0002]

2. Description of the Related Art 1) Strength, 2) Corrosion resistance, 3) Fracture mechanical properties (fatigue crack propagation resistance, fracture toughness, etc.), 4) are required for outer panels and structural materials of automobiles and other transportation equipment. Press formability is mentioned, and recent development trends of materials include not only strength but also comprehensive evaluation including material manufacturing, assembly of members, and operation.

Conventionally, as a high strength aluminum alloy, Al--Cu--Mg (2000 series) or Al--Zn-- has been used.
Although Mg—Cu (7000 series) aluminum alloys are known, these alloys are excellent in strength, but they are not necessarily sufficient in workability and corrosion resistance, and there are difficulties in production. On the other hand, Al-Mg-Si-based (6000 series) aluminum alloys are generally inferior in strength to the above high-strength aluminum alloys, but are superior in terms of corrosion resistance and moldability,
In addition, 2000 series and 7000 series alloys must be molded in the O tempered state, and after the molding, solution treatment, quenching, and strain correction must be taken, whereas 6000 series alloys are molded with T4 tempering. Since it can be carried out and can be put into practical use only by performing a tempering treatment after molding, there is also an advantage that the manufacturing cost can be reduced.

Under the circumstances, attempts have been made to improve the strength characteristics of 6000 series aluminum alloys, and 6013 alloy, 6056 alloy, 6082 alloy and the like, which have higher strength than the conventional 6061 alloy, have been developed. As an aluminum alloy with strength and toughness, Si: 0.9-1.8%, Mg: 0.8-1.4
%, Cu: 0.4 to 1.8% (however, Si content-Mg
Content / 1.73 ≧ 0.3%) and Mn: 0.05-0.8
%, Cr: 0.05 to 0.35%, Zr: 0.05 to 0.20% of 2
Alloys containing more than one species and the balance aluminum and inevitable impurities have also been developed. (Japanese Patent Laid-Open No. 59-50147)

Further, as a 6000 series aluminum alloy which is excellent in formability and bake hardenability and is suitable for applications such as automobile parts, Cu: 1.5 to 2.5 wt%, Mg: 0.5 to 1.0 wt%, Si:
0.3-1.0wt%, Ti: 0.005-0.05wt%, B: 0.0005-
0.03wt% included, Mn, Cr, V, Zr 0.04wt alone
% Or less, two or more kinds in total of 0.09 wt% or less and Fe of 0.
An aluminum alloy which is regulated to 25 wt% or less and whose balance of Si / Mg is 1.1 or less and which consists essentially of Al and whose longest side length of crystallized substance is 13 μm or less is also proposed. There is. (Japanese Patent Publication No. 61-39391)

Outer panels of transportation equipment such as automobiles are of course required to have excellent strength characteristics, but are also required to have good workability because they are subjected to press molding under various conditions. Since it may be exposed to a severe corrosive environment during driving, it must have excellent corrosion resistance and should not cause fatigue failure in a corrosive environment. It is necessary for the material for the outer plate to have these properties in a well-balanced manner. Due to the sophistication of technology, there are cases where even a slight difference has an importance that cannot be ignored, and if any of the characteristics is inferior even a little, it means that comprehensive evaluation as a material cannot be obtained.
From such a viewpoint, it cannot be said that the above 6000 series aluminum alloy does not necessarily have satisfactory performance, particularly when it is applied as an automobile outer plate.

[0007] One of the inventors is the above-mentioned 6000
Si:
It contains 0.5-1.5%, Mg: 0.9-1.6%, Cu: 1.2-2.5%, and the quantitative relationship of these alloying elements is 3 ≤ Si% +
Mg% + Cu% ≦ 4, Mg% ≦ 1.7 × Si%, Cu% / 2
A high-strength aluminum alloy excellent in formability and corrosion resistance, which has a composition specified as a relationship satisfying ≦ Mg% ≦ (Cu% / 2) +0.6, is proposed. (Japanese Patent Application No. 6-121937)

[0008]

SUMMARY OF THE INVENTION The present invention is based on the above alloys in order to further improve the properties of the above-proposed high-strength aluminum alloys, particularly the combination of the components contained, the composition range, and the relationship among the components. The present invention has been made as a result of further studies, and its purpose is to provide an aluminum alloy having particularly excellent corrosion resistance, as well as formability and high strength.

[0009]

The high-strength aluminum alloy excellent in formability and corrosion resistance according to the present invention for achieving the above-mentioned object is a weight percentage of Si: 0.5 to 1.5%, M:
g: 0.9-1.5%, Cu: 1.2-2.4%, conditional expression, 3 ≤ S
i% + Mg% + Cu% ≦ 4, Mg% ≦ 1.7 × Si%, C
Si satisfying u% / 2 ≦ Mg% ≦ (Cu% / 2) +0.6,
Contains Mg and Cu, further contains Cr: 0.02 to 0.4%, and limits Mn as an impurity to 0.05% or less,
The basic characteristic of the structure is that the balance is Al and unavoidable impurities.

In addition, Zr: 0.03 to 0.2%, V: 0.03 to 0.2% and Zn:
One or more of 0.03 to 2.0%, and Ti: 0.005 to 0.1% and B: 1 to 50 ppm as other optional components.
The second and the first structural elements that contain at least 2000 species / two species, and that the precipitates having a diameter of 0.01 μm or less and a length of 0.3 μm or less are distributed in the structure of the aluminum alloy in an amount of 2000 / μm ² or more. The third and fourth characteristics.

Further, by heating to a temperature range of 500 to 580 ° C
Solution treatment is performed for 60 minutes or less, quenching treatment is performed at a cooling rate of 10 ° C / s or more, and aging is performed for 2 weeks at room temperature. The limit bending radius is 1T or less (T is the plate thickness),
After the solution treatment that is heated in the temperature range of 500 to 580 ℃ and kept for 60 minutes or less, and cooled at a cooling rate of 10 ℃ / s or more, after quenching treatment, with or without forming,
Heat treated at 170-200 ℃ for 2-24h, JIS W
The corrosion weight loss in the intergranular corrosion test specified in 1103
The fifth and sixth features of the invention are that it is 0.6% or less.

[0012] Explaining the significance of each component addition and the reason for limitation in the aluminum alloy of the present invention, Si coexists with Mg to form a fine intermetallic compound Mg ₂ Si to enhance the strength of the alloy. If the Si content is less than 0.5%, sufficient strength cannot be obtained, and if the Si content exceeds 1.5%, the corrosion resistance of the alloy decreases. Therefore, the Si content range is 0.5-1.
5% is preferred. The range is more preferably 0.7 to 1.2%.

Mg coexists with Si to precipitate Mg ₂ Si, and coexists with Cu to finely precipitate the compound CuMgAl ₂ to improve the strength of the alloy. If the content of Mg is less than 0.9%, a sufficient effect cannot be obtained, and if it exceeds 1.5%, the corrosion resistance decreases. Therefore, the content range of Mg is 0.
9 to 1.5% is preferable. More preferably, it is in the range of 1.0 to 1.2%.

Cu, like Si and Mg, is an element that contributes to improving the strength of the alloy. If the content is less than 1.2%, the effect is not sufficient, and if it exceeds 2.4%, the corrosion resistance of the alloy decreases. Therefore, the Cu content range is preferably 1.2 to 2.4%. It is more preferably in the range of 1.5 to 2.0%. Cr
Improves the formability by refining the structure of the alloy and contributes to the improvement of corrosion resistance. The preferred content range is 0.02
0.4%, the effect is not sufficient below 0.02%, 0.4
If it exceeds%, a coarse intermetallic compound is likely to be formed and the formability is deteriorated.

[0015] Mn refines the crystal grains to improve the alloy strength, but Mn-based intermetallic compounds are generated, and this Mn
In the present invention, Mn is 0.05% or less, preferably 0.02%, because the system compound serves as a starting point of pitting corrosion and accelerates corrosion.
It is important to limit the content to 0.01% or less, more preferably 0.01% or less.

In the present invention, as described above, Si, Mg, C
Although u is contained as an essential component, regarding these components, the conditional expression, 3 ≦ Si% + Mg% + Cu% ≦
4, Mg% ≦ 1.7 × Si%, Cu% / 2 ≦ Mg% ≦ (Cu
% / 2) +0.6 is an essential requirement, and under these conditions, a preferable dispersed state of the intermetallic compound that gives strength and formability to the alloy can be obtained without lowering the corrosion resistance of the alloy material. If the total content of Si, Mg and Cu is less than 3%, it is difficult to obtain a preferable dispersion of the compound, and if it exceeds 4%, the corrosion resistance of the alloy is deteriorated. In addition, the quantitative relationship between Mg and Si is Mg% ≦ 1.7 × Si%, and the quantitative relationship between Mg and Cu is Cu.
% / 2 ≦ Mg ≦ (Cu% / 2) +0.6
The amount of the intermetallic compound produced and the distribution state are controlled, and the alloy can be provided with well-balanced strength characteristics, formability, and corrosion resistance.

Zr, V and Zn added as selective components form an intermetallic compound to make the grain size of the alloy fine and improve the strength of the alloy. The preferable addition amount is Zr: 0.03 to 0.2%, V: 0.03 to 0.2%, Z
n: 0.03 to 2.0%. If the added amount of these components is less than the lower limit, the effect is small, and if added in excess of the upper limit, the formation of coarse intermetallic compounds increases and the formability and corrosion resistance deteriorate.

Ti and B added as other optional components
Prevents the ingot cracking by refining the cast structure. It also improves the formability, especially Ti improves the formability without changing the corrosion resistance of the alloy. The preferable addition range is Ti: 0.005
.About.0.1%, B: 1 to 50 ppm. If the amount added is less than the lower limit, the effect is small, and if it exceeds the upper limit, the formation of coarse intermetallic compounds increases and the formability decreases.

In the present invention, Si and M are used as essential alloy components.
g, Cu, Cr are contained, Mn is limited to a certain amount or less, and Zr, V, Zn, and Ti, B are added as selective components to form an intermetallic compound between the respective components in the alloy structure. By finely precipitating and controlling their precipitation amount and distribution state, it is possible to obtain a material excellent in strength, formability, and corrosion resistance.
Precipitates with a size of 0.01 μm or less and a length of 0.3 μm or less
By distributing a precipitation amount of 2000 particles / μm ² or more, it is possible to give the alloy material a better balance of properties.

The aluminum alloy of the present invention can be supplied not only as a plate material, but also as an extruded material, a forged material, etc. A preferred method for producing a plate material will be described. An ingot is made by semi-continuous casting, and the obtained ingot is homogenized at a temperature of 500 ° C or higher and lower than the melting point. If the homogenization temperature is less than 500 ° C, the ingot segregation is not sufficiently removed, and Mg that contributes to the strength
₂ The solid solution of Si and Cu becomes insufficient, the strength becomes low, and the moldability tends to decrease. Then, hot rolling is started at a temperature of 400 ° C or higher, and hot rolling is ended at a temperature of 200 to 350 ° C.
If the starting temperature of hot rolling is less than 400 ℃, M
G ₂ Si is likely to be coarsely precipitated, which makes it difficult to form a solid solution in the solution treatment, which causes a decrease in strength. The end temperature of hot rolling is
If it is less than 200 ° C, the surface of the water-soluble rolling oil used in hot rolling tends to remain, resulting in poor surface quality. If the temperature exceeds 350 ° C, the structure becomes coarse due to secondary recrystallization during rolling and the anisotropy increases.

After hot rolling, with or without intermediate annealing, or by cold rolling the hot rolled material to a predetermined thickness, then intermediate annealing, and finally cold rolling with a workability of 60% or more. I do. If the workability of cold rolling is less than 60%, the crystal grains are likely to become coarse, and roughening is likely to occur during the forming process.
Further, the decomposition of the hot-rolled structure is insufficient and the formability is poor. After cold rolling, heat treatment at a temperature rising rate of 5 ° C / s or more to a temperature range of 500 to 580 ° C and holding for 60 minutes or less is subjected to solution treatment, and then quenching is performed at a cooling rate of 10 ° C / s or more. Perform processing.

If the temperature rising rate in the solution treatment is less than 5 ° C./s, the crystal grains become coarse and the skin is likely to be roughened during the molding process. If the holding temperature is less than 500 ° C, the solid solution of precipitates becomes insufficient, resulting in poor strength and moldability. If it exceeds 580 ° C, local eutectic melting may impair the workability. Further, since the performance that can be reached is saturated when the holding time in the solution heat treatment exceeds 60 minutes, holding for 60 minutes or more reduces productivity. If the cooling rate during the quenching treatment is less than 10 ° C / s, the compound precipitates in an undesired distribution state, the ductility decreases, and the corrosion resistance, strength, and formability are impaired.

The aluminum alloy material of the present invention has excellent formability even after being aged at room temperature (T4 temper) after quenching.
Heat treatment at 170-200 ℃ for 2-24h. Heat treatment temperature is 1
If the temperature is lower than 70 ° C, heat treatment for a long time is required to obtain the desired performance, which is not preferable in industrial production, and heat treatment at a temperature higher than 200 ° C lowers the strength. If the heat treatment time is less than 2 hours, sufficient strength cannot be obtained, and if it exceeds 24 hours, the strength begins to decrease. An aluminum alloy that has a structure in which precipitates with a diameter of 0.01 μm or less and a length of 0.3 μm or less are 2000 pieces / μm ² or more are distributed by combining the above alloy composition and manufacturing conditions, and that strength, formability and corrosion resistance are excellent. The material is obtained.

[0024]

In the present invention, specific amounts of Si, Mg, Cu
And Cr are contained as essential components, the amount of Mn is limited, Zr, V and Zn, and Ti and B are selectively added, and the content range of Si, Mg and Cu is limited by a predetermined relational expression. Provides a desirable precipitation state of the intermetallic compound formed between the Al and alloy components of the matrix, and the combination of this component and the structure further improves corrosion resistance while maintaining excellent strength and formability. . Particularly excellent material properties can be achieved by using a structure in which precipitates having a diameter of 0.01 μm or less and a length of 0.3 μm or less are distributed in 2000 or more / μm ² .

[0025]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1 The aluminum alloys shown in Table 1 were ingot-cast by semi-continuous casting, after the surface cutting of the casting surface of the ingot, homogenization treatment was performed at a temperature of 525 ° C for 8 hours, and then hot rolling was performed at this temperature. Start and thickness 4.
It was set to 5 mm, and hot rolling was completed at 325 ° C. Subsequently, cold rolling was performed to obtain a final plate thickness of 1.0 mm. At 530 ° C
After the solution treatment for 10 minutes, quenching treatment was performed by cooling with water.

[0026]

[Table 1] << Table Note >> B content is ppm

After the hardening treatment, two weeks after aging at room temperature, a tensile test and a bending test were performed as a T4 temper, and after the hardening treatment, a tensile test was performed as a T6 temper after a tempering treatment at 180 ° C. for 6 hours. Further, the T6 tempered material was subjected to an intergranular corrosion test specified in JIS W 1103. The test results are shown in Table 2. As can be seen from Table 2, the alloy materials according to the present invention all exhibit excellent tensile properties, formability and corrosion resistance, and particularly T4 tempered materials have an elongation of 26% or more and a 180 ° of 1.0 mm or less.
It had a limit bending radius. As a typical example, alloy material N
When the structures of o.1 T4 tempered material and T6 tempered material were observed with an electron microscope and precipitates in the structure were observed, the diameter was 0.01
2000 deposits with μm or less and 0.3 μm or less in length
/ μm ² was exceeded.

The details of the intergranular corrosion test according to JIS W 1103 are as follows. After cleaning the alloy material, NaCl57
g and 30% H ₂ O ₂ in 30 ℃ test solution adjusted to 1 liter with water
After soaking for 6 hours, measure the corrosion weight loss.

[0029]

[Table 2]

Comparative Example 1 Aluminum alloy sheet materials (sheet thickness: 1.2 mm) having the compositions shown in Table 3 were produced in the same steps as in Example 1, and the tensile test, bending test and intergranular corrosion were performed in the same manner as in Example 1. The test was conducted. The results are shown in Table 4. Those that do not satisfy the conditions of the present invention are underlined.

[0031]

[Table 3] << Table Note >> (1) B content is ppm (2) Alloy material No. 7 is Si + Mg + Cu> 4 (3) Alloy material No. 8 is Si + Mg + Cu <3 (4) Alloy material No. 9 is Mg> 1.7 × Si (5) alloy material No.10 is Cu / 2 <Mg (6) alloy material No.11 is Mg> (Cu / 2) +0.6

[0032]

[Table 4]

As can be seen from Table 4, those which deviate from the alloy composition limits of the present invention are inferior in strength, formability, or corrosion resistance. Alloy material No. 7 has a total amount of Si, Mg, and Cu of more than 4, and therefore has poor corrosion resistance and poor formability. Alloy material No. 8 has a low strength because the total amount of Si, Mg and Cu is less than 3. Alloy material No. 9 does not satisfy the relational expression between Mg and Si, and therefore has poor formability and corrosion resistance. Alloy material N
Since o.10 to 11 do not satisfy the relational expression between Mg and Cu, formability and corrosion resistance are poor, and alloy material No. 11 has insufficient strength. Alloy material No. 12 has a poor Mn content because the Mn content exceeds the limit value, and alloy material No. 13 has a small amount of Cr and is an alloy material.
In Nos. 14 to 17, the content of the selected component exceeds the limit value, so that either moldability or corrosion resistance is poor.
When the texture of the T6 tempered material was observed with an electron microscope for these alloy materials, the alloy material Nos.
20 precipitates with a size of 0.01 μm or less and a length of 0.3 μm or less
It was less than 00 lines / μm ² .

[0034]

As described above, according to the present invention, strength,
An aluminum alloy material having excellent formability and corrosion resistance is provided, and it is useful as an outer plate for transportation equipment such as automobiles.

Claims (6)

[Claims] 1. Si: 0.5 to 1.5 in% by weight (the same applies hereinafter)
%, Mg: 0.9 to 1.5%, Cu: 1.2 to 2.4%, conditional expression, 3
≦ Si% + Mg% + Cu% ≦ 4, Mg% ≦ 1.7 × Si
%, Cu% / 2 ≦ Mg% ≦ (Cu% / 2) +0.6, Si, Mg and Cu are contained, and Cr: 0.02 to 0.
A high-strength aluminum alloy that contains 4%, limits Mn as an impurity to 0.05% or less, and is composed of the balance aluminum and unavoidable impurities and has excellent formability and corrosion resistance. 2. The aluminum alloy contains Zr: 0.03 to 0.2.
%, V: 0.03 to 0.2% and Zn: 0.03 to 2.0%, at least one of which is contained in the high strength aluminum alloy excellent in formability and corrosion resistance. 3. The aluminum alloy contains Ti: 0.005 to 0.1.
%, B: 1 type or 2 types of 1 to 50 ppm are contained, The high strength aluminum alloy excellent in formability and corrosion resistance according to claim 1 or 2. 4. The diameter of 0.01 in the structure of the aluminum alloy.
The high-strength aluminum alloy excellent in formability and corrosion resistance according to claim 1, wherein precipitates having a size of less than or equal to μm and a length of less than or equal to 0.3 μm are distributed in a number of 2000 / μm ² . 5. A solution treatment of heating to a temperature range of 500 to 580 ° C. and holding for 60 minutes or less, a quenching treatment of cooling at a cooling rate of 10 ° C./s or more, and an aging at room temperature for 2 weeks. The elongation after processing is 26% or more, and the 180 ° critical bending radius is
It is 1T or less (T is the plate thickness), which is characterized in that
A high-strength aluminum alloy having excellent formability and corrosion resistance as described. 6. A solution treatment for heating to a temperature range of 500 to 580 ° C. and holding for 60 minutes or less, a quenching treatment for cooling at a cooling rate of 10 ° C./s or more, and a molding process, or 5. After performing a heat treatment for 2 to 24 hours at a temperature of 170 to 200 [deg.] C. without performing it, the corrosion weight loss in the intergranular corrosion test according to JIS W 1103 is 0.6% or less. High strength aluminum alloy.